LeetCode： Single Number II

Question

Given an integer array nums where every element appears three times except for one, which appears exactly once. Find the single element and return it.

Example 1:

Input: nums = [2,2,3,2]

Output: 3

Example 2:

Input: nums = [0,1,0,1,0,1,99]

Output: 99

Constraints:

1 <= nums.length <= 3 * 104

-231 <= nums[i] <= 231 - 1

Each element in nums appears exactly three times except for one element which appears once.

Solution

def single_number(nums)
  data_set = Hash.new(0)
  nums.each do |num|
    data_set[num] += 1
  end
  data_set.key(1)
end